1. Technical Field
This invention relates to an in-tire sound absorber for the reduction of tonal sounds in pneumatic tires.
2. Description of the Related Art
Tonal sound is caused by a standing wave generated in the space between the tire and wheel rim. This standing wave relates to the geometry of the tire, and the temperature and pressure of the air in the tire cavity. The resultant tone or sound is typically below 600 Hz.
The problem of tonal noise transmission into the motor vehicle cabins has been addressed by a number of means. U.S. Pat. No. 6,755,483 (Sumitomo Rubber Industries, Ltd.) describes the use of a noise damper disposed in the cavity formed between the rim and the tire. The noise damper is made from porous material which has a specific density of between 0.005 and 0.06 and in particular an open-cell polyurethane foam. In one embodiment, the noise damper has an uneven facing, or is made from an outer layer having low sound reflection and an inner layer, adjacent the wheel rim, having high sound absorption.
However, it is often a problem with the prior art that the noise damper can be damaged during fitment of the tire on the wheel rim or the noise damper is not physically strong enough to resist tearing or breaking apart during normal operation.